21378657 has 8 divisors (see below), whose sum is σ = 28564000. Its totient is φ = 14222880.

The previous prime is 21378653. The next prime is 21378659. The reversal of 21378657 is 75687312.

It is a sphenic number, since it is the product of 3 distinct primes.

It is not a de Polignac number, because 21378657 - 2² = 21378653 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21378653) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 5644 + ... + 8637.

It is an arithmetic number, because the mean of its divisors is an integer number (3570500).

Almost surely, 2^21378657 is an apocalyptic number.

It is an amenable number.

21378657 is a deficient number, since it is larger than the sum of its proper divisors (7185343).

21378657 is a wasteful number, since it uses less digits than its factorization.

21378657 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 14783.

The product of its digits is 70560, while the sum is 39.

The square root of 21378657 is about 4623.7059811368. The cubic root of 21378657 is about 277.5407812803.

The spelling of 21378657 in words is "twenty-one million, three hundred seventy-eight thousand, six hundred fifty-seven".